<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./js/vue.js"></script>
</head>

<body>
    <div id="app">
        <button @click="add">{{price}}</button>
    </div>
</body>
<script>
    const vm = new Vue({
        el: '#app',
        data: {
            price:100
        },
        methods: {
            add(){
                this.price+=10;
            }
        },
        watch: {
            price(newVal){
                console.log(newVal-100);
                
            }
        }
    })
</script>

</html>